The SensesThe Senses

The Olfactory and The Olfactory and Optical/Visual SensesOptical/Visual Senses

(Smell and Sight)(Smell and Sight)

General Senses:General Senses:

• Temperature• Pain• Touch• Pressure• Vibration• Proprioception (body position)

– The receptors for these senses are distributed throughout the body

Special SensesSpecial Senses

• Olfaction• Gustation (taste)• Vision• Equilibrium (balance)• Hearing

– These receptors are located within specific structures

Sensory ReceptorsSensory Receptors

• Specialized cells that, when stimulated, sends a sensation to the CNS– Simple receptors are free nerve endings– Complex receptors are specialized to

respond to only specific stimuli

Sensory InformationSensory Information

• Relayed by action potentials traveling through sensory fibers (collection of axons)

• Increase stimulus = Increase frequency of action potentials

– Interpreted by the CNS depending on the area of the brain that is stimulated

• A reduction in sensitivity in the presence of a constant stimulus– Due to changes in receptor sensitivity or

inhibition along the sensory pathway

AdaptationAdaptation

• Location:– Nasal cavity on either side of the nasal

septum– Inferior to the cribiform plate of the ethoid

bone

• Structure:– Olfactory epithelium

• Olfactory receptors (neurons sensitive to chemicals)

• Supporting cells• Basal stem cells

OlfactionOlfaction

• Secrete mucus to prevent a build-up of dangerous or overpowering stimuli

• Also keeps the area moist and free of debris

Olfactory GlandsOlfactory Glands

• Highly modified neurons with elongated cilia (between 10-20 million receptors in an area 5 sq. cm)

• Canines have 72 times greater surface area than humans in their olfactory organs = better smellers

ReceptorsReceptors

• Axons penetrate the cribiform plate• Trigger the olfactory bulbs• Travel along the olfactory tract• Reach the olfactory cortex of the

cerebrum• Also affect the hypothalamus and

parts of the limbic system

Olfactory PathwayOlfactory Pathway

How “smell” worksHow “smell” works

• Olfactory stimuli is the only sensory information to reach the cerebral cortex without first synapsing in the thalamus. The connections to the limbic system and the hypothalamus help explain the emotional and behavioral responses triggered by smells.

Fun FactFun Fact

Visual (the eye)Visual (the eye)

The RetinaThe Retina

• The neural tunic: contains several layers of cells, the outermost layer contains the photoreceptors– Photoreceptors: detect photons of light…humans

only sensitive to the spectrum of visible light

RodsRods

• Do not discriminate color…only provide the CNS with info about the presence or absence of photons

• Very light sensitive and enable us to see in dim light (enhanced in most animals)

• Located around the sides of the retina (approx. 12 million)

ConesCones

• Color vision- provides info about the wavelength of photons

• Three types: red, blue, green- in different combinations provide the perception of different colors– Color blindness= one ore more classes of cones

are absent or not functioning

• Located in the macula lutea with the highest concentration in fovea – when you look directly at an object this is where the image falls on the retina

Bipolar CellsBipolar Cells

• Cells that synapse with the rods and Cells that synapse with the rods and cones (roughly 6 million)cones (roughly 6 million)

Ganglion CellsGanglion Cells•Synapse with the bipolar cells and Synapse with the bipolar cells and relay information to the brainrelay information to the brain

Horizontal and Amacrine Horizontal and Amacrine CellsCells

• Regulate communication between photoreceptors and ganglion cells, adjust sensitivity of the retina by sending inhibitory or excitatory signals

Optic DiscOptic Disc

• The origin of the optic nerve, next to the fovea, also has blood vessels and lacks photoreceptors– The blind spot

Lens and Visual Lens and Visual AccommodationAccommodation

• Accommodation- focusing the image on the retina by changing the shape of the lens

– Rounder = focuses the image of a nearby object

– Flatter = focuses a distant object

Accommodation ProblemsAccommodation Problems

• Astigmatism: – irregularities in the shape of the lens or

cornea

• Myopia: – “near-sightedness”; the eye is too deep

so images focus in front of the retina• Corrected by a diverging lens

• Hyperopia:– “Farsightedness”; The eye is too shallow

so images focus past the retina• Corrected with a converging lens

Masters of IllusionMasters of Illusion

Focus on the dot and move Focus on the dot and move your head side to side or your head side to side or

forward to back…forward to back…

How many legs does the How many legs does the elephant have?elephant have?

Stare at the black dot and watch the haze disappear…

Shapes that don’t existShapes that don’t exist

The Kaniza The Kaniza EffectEffect

What do you see?What do you see?

The Impossible TridentThe Impossible Trident

Straight or Crooked?Straight or Crooked?

Count the Black DotsCount the Black Dots

Circles or Spirals?Circles or Spirals?

http://www.sapdesignguild.org/resources/optical_illusions/images/couple.gif

Crooked or Straight?Crooked or Straight?

http://www.is.svitonline.com/malinman/optic/spirkrug.gif

Optical Illusions in ShapesOptical Illusions in Shapes

Floating Sphere?Floating Sphere?

Make ‘em stop spinning!!Make ‘em stop spinning!!

Image CreditsImage Credits• http://waynesword.palomar.edu/images/blckdots.jpg

• http://www.is.svitonline.com/malinman/optic/spirkrug.gif• http://www.sapdesignguild.org/resources/optical_illusions/images/couple.gif

• http://waynesword.palomar.edu/images/lines.jpg• http://www.eyesearch.com/optical.vase.gif

• http://www.sackville.ednet.ns.ca/art/gallery/exhibit/draw/Escher,M.C.-Relativity-1953.jpg• http://www.math.technion.ac.il/~rl/M.C.Escher/2/escher-hands.gif

• http://www.cbu.edu/~jvarrian/252/eye.gif• http://www.city.ac.uk/colourgroup/spectrum.gif

• http://medweb2.bham.ac.uk/image_database/bain/images/229339c.jpghttp://medweb2.bham.ac.uk/image_database/bain/images/229339c.jpg• http://www.eyesearch.com/astigmatism.jpghttp://www.eyesearch.com/astigmatism.jpg• http://www.whiteeye.net/images/myopia.jpghttp://www.whiteeye.net/images/myopia.jpg

• http://www.colorado.edu/epob/epob1220lynch/image/figure6n.jpghttp://www.colorado.edu/epob/epob1220lynch/image/figure6n.jpg• http://www.rktekt.com/ck/im/FineArt/eye.jpghttp://www.rktekt.com/ck/im/FineArt/eye.jpg• http://mathworld.wolfram.com/gifs/ouchi.gifhttp://mathworld.wolfram.com/gifs/ouchi.gif

• http://www.aetheronline.com/mario/images/Favourite%20Images/Optical%20Illusions/14_jpg.jpghttp://www.aetheronline.com/mario/images/Favourite%20Images/Optical%20Illusions/14_jpg.jpg• http://www.mercola.com/2003/sep/27/illusion4.gifhttp://www.mercola.com/2003/sep/27/illusion4.gif• http://members.cox.net/mystic-warrior/mag2.jpghttp://members.cox.net/mystic-warrior/mag2.jpg